CN108088885B - Soil heavy metal electrochemical in-situ detection system and detection method - Google Patents
Soil heavy metal electrochemical in-situ detection system and detection method Download PDFInfo
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- CN108088885B CN108088885B CN201711105807.1A CN201711105807A CN108088885B CN 108088885 B CN108088885 B CN 108088885B CN 201711105807 A CN201711105807 A CN 201711105807A CN 108088885 B CN108088885 B CN 108088885B
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Abstract
The invention provides a soil heavy metal electrochemical in-situ detection system, which comprises: the system comprises a three-electrode sensor, signal acquisition and processing equipment and an upper computer control system, wherein the signal acquisition and processing equipment comprises an STM32 microcontroller and a minimum system thereof, a digital-to-analog converter, an analog-to-digital converter, a potentiostat module, a serial communication module and a sensor connecting port. The invention also provides an electrochemical in-situ detection method for the heavy metals in the soil. The soil heavy metal electrochemical in-situ detection system provided by the invention integrates stripping voltammetry signals and a background current recognition algorithm, has an independent electrode cleaning function and an actual sample pretreatment function, has three heavy metal analysis methods, and can meet different detection requirements. The method can accurately detect the contents of heavy metal lead and cadmium in the soil sample, and overcomes the defects of the existing heavy metal detection method and technology in soil heavy metal detection.
Description
Technical Field
The invention belongs to the technical field of detection, and particularly relates to a detection system and a detection method for heavy metal ions in soil.
Background
In recent years, with the rapid development of industry, agriculture and transportation industry, harmful heavy metals (such as Zn, Cu, Pb, Cd, Cr and the like) entering soil environment through various ways are increasing, so that increasingly serious pollution and harm are caused to agricultural products, and the improvement of living standard also prompts people to pay more attention to the sanitary quality problem of fruits and agricultural products. The soil environment directly influences the growth, development and quality of plants, when heavy metals are accumulated to a certain degree, the soil is polluted, the growth, development and quality of fruit trees and agricultural products are influenced, and then harm is caused to human health through a food chain.
The traditional soil heavy metal detection at home and abroad usually adopts field sampling and then detection and analysis are carried out by a laboratory chemical kit instrument. At present, the domestic standard method for sudden heavy metal detection is mainly to carry out heavy metal detection by adopting a spectrum method after strong acid digestion treatment. The laboratory detection method has high accuracy, but has long detection period, complex operation, high detection cost and easy secondary pollution generation in the detection process, needs special personnel for operation and cannot simultaneously measure various heavy metals. Therefore, an automatic, comprehensive and accurate soil heavy metal detection system is developed, can be used for in-situ rapid detection of soil heavy metals, and has very important significance in the aspects of food, medicine, environmental monitoring and the like.
Disclosure of Invention
The invention aims to solve the existing problems and provides a soil heavy metal electrochemical in-situ detection system, which integrates stripping voltammetry signals and a background current recognition algorithm, has an independent electrode cleaning function and an actual sample pretreatment function, has three heavy metal analysis methods and can meet different detection requirements.
The second purpose of the invention is to provide an electrochemical in-situ detection method for heavy metals in soil.
The technical scheme for realizing the aim of the invention is as follows:
an electrochemical in-situ detection system for heavy metals in soil, comprising: a three-electrode sensor, a signal acquisition and processing device and an upper computer control system,
the signal acquisition and processing equipment comprises an STM32 microcontroller and a minimum system thereof, a digital-to-analog converter, an analog-to-digital converter, a potentiostat module, a serial port communication module and a sensor connecting port;
the STM32 microcontroller is connected with a digital-to-analog converter, the digital-to-analog converter is connected with a potentiostat module, and the potentiostat module is connected with a counter electrode and a reference electrode of the three-electrode sensor;
the working electrode of the three-electrode sensor is connected with the analog-to-digital converter, the analog-to-digital converter is connected with the STM32 microcontroller, and the serial port communication module is connected with the upper computer control system.
In the three-electrode sensor, a working electrode is one of a glassy carbon electrode, a carbon paste electrode and a screen printing electrode, and a reference electrode is an Ag/AgCl reference electrode; the counter electrode is a platinum wire electrode.
Wherein, three modules of a standard addition method, a standard model method and a double stripping voltammetry are displayed on a human-computer interaction interface of the upper computer control system. And/or, an electrode cleaning module and a sample pretreatment module.
An electrochemical in-situ detection method for heavy metals in soil comprises the following steps:
s1, determining the dissolution peak potential of heavy metal ions by using standard solution of known heavy metal components, and determining background current; the standard solution contains cadmium, lead, bismuth and copper ions (Cd)2+、Pb2+、Cu2+、Bi3+)，
S2, putting a soil sample leaching solution into the three-electrode sensor, and setting S-G smoothing and stripping voltammetry parameters;
s3, detecting the heavy metal content by one of a standard addition method, a standard model method and a double stripping voltammetry.
Wherein the operation of determining the dissolution peak potential of the heavy metal ions comprises the following steps: performing stripping voltammetry on a standard solution with known heavy metal components, wherein the obtained stripping voltammetry data is Y (N), and if Y (N) -Y (N-1) > 0 and Y (N +1) -Y (N) < 0 at the point N, the corresponding potential of the point is a stripping potential, the current of the point is a stripping current, and the stripping peak potentials of different heavy metal ions are stored in an upper computer control system;
the parameters of the stripping voltammetry measurement were: initial potential is-1.0 to-1.5 Vvs. Ag/AgCl, termination potential is 0.1 to 0.3Vvs. Ag/AgCl, frequency is 10 to 50Hz, standing time is 5 to 20s, potential increment is 0.001 to 0.01V, amplitude is 0.02 to 0.03V, cleaning potential is 0.2 to 0.5Vvs. Ag/AgCl, cleaning time is 100 plus 300s, deposition potential is-1.0 to-1.5 Vvs. Ag/AgCl, and deposition time is 80 to 200 s.
Wherein the operation of determining the background current is: determining the dissolution peak potential of the heavy metal ions, wherein the dissolution peak potential within +/-0.2V is the dissolution peak potential range; according to the formula
Determining the slope between each point, searching two closest slopes in the dissolution peak potential range of the heavy metal ions, connecting the two closest slopes to obtain a tangent, drawing a vertical line perpendicular to the X axis from the dissolution peak potential, and taking the ordinate of the intersection point of the vertical line and the tangent as the background current.
The dissolution peak potential range of each heavy metal ion is set on an upper computer control system. Because the dissolution peak of the heavy metal corresponding to each sensor (i.e. the electrode modified by different materials) will shift, and different actual samples will also shift the dissolution peak during the detection process. According to actual conditions, different sensors and detection environments can be flexibly handled by setting through the upper computer control panel.
Wherein, in step S2, stripping voltammetry parameters are set as follows: the deposition potential is-1.0 to-1.5V, the deposition time is 120-ion-150 s, the standing time is 5 to 15s, the scanning starting voltage is-1.5 to-1.0 Vvs. Ag/AgCl, the termination voltage is 0.1 to 0.2Vvs. Ag/AgCl, the potential increment is 0.001 to 0.01V, the pulse frequency is 20 to 30Hz, the sampling time is 0.01 to 0.05s, and the pulse amplitude is 0.02 to 0.05V.
The first preferred technical scheme of the invention, the standard addition method, comprises the following steps:
1) firstly, carrying out first detection on an actual sample leaching liquor with unknown concentration (clicking a 'first detection' button in a standard addition method module), automatically carrying out peak searching analysis by an upper computer control system to obtain the peak current of target detection ions, displaying the peak current on an interface, recording the current Y0, and carrying out the labeling concentration value of 0, namely, not carrying out the labeling.
2) Quantitatively adding a standard solution into an actual sample with unknown concentration, inputting a first standard adding concentration in an input frame (clicking a 'second detection' button in a standard addition method module), carrying out second detection, and automatically carrying out peak searching analysis by an upper computer control system to obtain a peak current Y1 of a target detection ion after first standard adding, wherein the standard adding concentration is X1;
3) quantitatively adding the standard solution again, inputting a second standard adding concentration in the input box, (clicking a 'third detection' button in the standard addition method module), carrying out third detection, automatically carrying out peak searching analysis by an upper computer control system, and obtaining the peak current of the target detection ion, wherein the peak current is recorded as Y2, and the standard adding concentration is 2X 1;
4) performing third-time labeling on the target actual sample leaching liquor, inputting third-time labeling concentration in an input box, (clicking a 'fourth-time detection' button in a standard addition method module), performing fourth-time detection, automatically performing peak searching analysis by an upper computer control system, and obtaining the peak current of target detection ions, wherein the peak current is marked as Y3, and the labeling concentration is 3X 1;
5) performing linear regression by using a least square method according to dissolution peak values Y0, Y1, Y2 and Y3 obtained by four times of detection and corresponding standard concentration;
6) after obtaining the regression equation, the upper computer automatically obtains the absolute value of the abscissa where the peak current (ordinate Y) is 0, and the absolute value is the predicted value of the concentration of the heavy metal in the sample.
The second preferred technical scheme of the invention, the operation of the standard model method, is as follows:
establishing a mathematical model of the peak value and the ion concentration by using a standard solution and taking the dissolution peak value as an independent variable and the ion concentration as a dependent variable, wherein the mathematical model is a unitary, binary or ternary equation, and the coefficient and constant term of the model are input into an upper computer control system; detecting a sample containing one to three types of modeled ions; the ions set by the model are cadmium, lead and copper ions.
For example, for a binary equation, the operation is: 1) inputting coefficients of primary terms X1 and X2, secondary terms X1X2 and X1 of the conventional model into the interface of the conventional model2And X22Coefficient and constant terms;
2) the detection interface is provided with two buttons for detecting cadmium ions and lead ions. When cadmium ions need to be detected, X1 and X2 are the peak values of the cadmium ions and the copper ions respectively, and corresponding model parameters corresponding to the cadmium ions and the copper ions are input from the panel. When lead ions need to be detected, X1 and X2 are the peak values of the lead ions and the copper ions respectively, and corresponding model parameters corresponding to the lead ions and the copper ions are input from the panel.
For example, in the standard model method, detection of cadmium ions and lead ions shares the same input interface, different dissolution peak values of heavy metal ions are obtained through different detection buttons, and upper computer software automatically substitutes the dissolution peak values into a model corresponding to model parameters for calculation.
The third preferred technical scheme of the invention, namely the operation of the double stripping voltammetry, comprises the following steps:
1) performing pre-deposition treatment on a soil leaching solution, placing a three-electrode sensor consisting of a graphite powder-paraffin oil carbon paste electrode and a reference electrode into the soil leaching solution, performing 500-700 s first pre-deposition on heavy metals in the soil leaching solution by applying a constant potential of 0.3V vsAg/AgCl, standing for 10-20 s after the deposition is finished, and taking out the three-electrode sensor to obtain a pre-treated soil leaching solution;
2) adding one or more of bismuth ions, cadmium ions and lead ions into the pretreated soil leaching liquor to enable the ion concentration to independently reach 5-600 mu g/L, carrying out first deposition, quickly transferring the three electrodes into a miniature electrolytic cell for first dissolution after the deposition is finished, adding a buffer solution with the pH value of 4.0-5.5 into the electrolytic cell in advance, and carrying out second dissolution voltammetry detection on heavy metals in the miniature electrolytic cell by using a three-electrode sensor consisting of a glassy carbon electrode, a reference electrode and a counter electrode to obtain a dissolution peak signal X0;
3) adding heavy metal with known concentration into the pretreated soil leaching liquor, wherein the solution concentration is Y1, repeating the step 1) (clicking a second detection button in the step) to perform second stripping voltammetry detection, and obtaining a stripping peak signal X1.
4) Adding heavy metal with known concentration into the pretreated soil leaching liquor, wherein the solution concentration is Y2, repeating the step 1) (clicking a third detection button in the step) to perform third stripping voltammetry detection, and obtaining a stripping peak signal X2.
5) And performing linear regression by using a least square method according to the concentration values Y0, Y1 and Y2 obtained by three times of detection and corresponding standard concentration X0, X1 and X2.
6) And (3) putting the three-electrode sensor into the sample solution to be detected, detecting for the fourth time, automatically identifying and obtaining the dissolution current of the heavy metal with unknown concentration in the solution to be detected by the upper computer system, substituting the dissolution current into the regression equation obtained in the step, calculating, and obtaining and displaying the detection result.
The invention has the beneficial effects that:
the soil heavy metal electrochemical in-situ detection system provided by the invention integrates stripping voltammetry signals and a background current recognition algorithm, has an independent electrode cleaning function and an actual sample pretreatment function, has three heavy metal analysis methods, and can meet different detection requirements. Therefore, the content of heavy metal lead and cadmium in the soil sample can be accurately detected, and the defects of the existing heavy metal detection method and technology in soil heavy metal detection are overcome. The detection equipment has the advantages of high portability, easy carrying, simple operation and low cost, and can be widely applied to actual detection in various fields.
The soil heavy metal electrochemical in-situ detection system provided by the invention has the advantages of high portability, easiness in carrying, simplicity in operation, low cost and wide detection range, and can be widely applied to actual detection in various fields. The technical achievement provides technical support for the aspects of detection, evaluation and the like of agricultural product producing areas in China, and has great application potential in the aspects of environmental emergency detection and rapid sample screening.
Drawings
FIG. 1 is a schematic diagram illustrating a soil heavy metal electrochemical in-situ detection system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a dissolution current identification and acquisition algorithm provided in accordance with an embodiment of the present invention;
FIG. 3 is a schematic diagram of a background current identification and acquisition algorithm provided in an embodiment of the present invention;
FIG. 4 is an interface of a host computer detection system according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a standard additive method detection provided by an embodiment of the present invention;
FIG. 6 is a schematic diagram of a standard model method for detection according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of the detection of double stripping voltammetry provided by the embodiment of the invention.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. It will be understood by those skilled in the art that the scope of the present invention is not limited to the specific embodiments, and various modifications and changes may be made without departing from the spirit of the present invention.
The means employed in the detailed description are, unless otherwise specified, all technical means which are conventional in the art.
Example 1
As shown in figure 1, the soil heavy metal detection system consists of a three-electrode system, a signal acquisition and processing device and an upper computer control system. The signal acquisition and processing equipment comprises an STM32 microcontroller and a minimum system thereof, a digital-to-analog converter, an analog-to-digital converter, a potentiostat module, a serial port communication module and a sensor connecting port; the STM32 microcontroller is connected with a digital-to-analog converter, the digital-to-analog converter is connected with a potentiostat module, and the potentiostat module is connected with a counter electrode and a reference electrode of the three-electrode sensor; the working electrode of the three-electrode sensor is connected with the analog-to-digital converter, the analog-to-digital converter is connected with the STM32 microcontroller, and the serial port communication module is connected with the upper computer control system.
The three-electrode system includes a working electrode, a reference electrode and an auxiliary electrode. The signal acquisition and processing equipment comprises an STM32 microprocessor, a digital-to-analog converter, an analog-to-digital converter, an I/V conversion circuit, a constant potential circuit and a serial port communication module. The STM32 microprocessor provides trigger signals for the three-electrode system and processes the electrical signals containing the detection information, and controls the whole signal acquisition and processing equipment through an I/O port. The digital-to-analog converter is used to convert the digital signal triggered by the STM32 microprocessor into an analog signal that is provided by a potentiostatic circuit to the desired potential between the working electrode and the reference electrode. The I/V conversion circuit converts the current signal collected by the working electrode into a voltage signal. The analog-to-digital converter converts analog electrochemical signals collected by the working electrode into digital signals, and then the digital signals are processed by the STM32 microprocessor and then detection information is sent to the upper computer control system through the serial port communication module. And the upper computer system processes the electric signal sent by the signal acquisition and processing equipment, further processes the electric signal, and finally obtains a heavy metal detection result and displays the heavy metal detection result on an upper computer interface.
Fig. 4 shows an upper computer detection system interface provided in the embodiment of the present invention. As shown in the figure, the upper computer software interface is mainly divided into a system control area, a parameter setting area, a background current setting area, a cleaning function setting operation area, a detection method selection operation area, a detection map display area and a detection result display area.
Furthermore, the system control area consists of a button for connecting the signal acquisition and processing equipment, a button for exiting the system, a button for storing the result and a button for terminating the measurement.
Specifically, after the button interface is clicked to display that the connection is successful, the upper computer system and the signal acquisition and processing equipment are in an online state, the system works normally, and detection can be performed. After clicking the quit system button, the system is closed and automatically quits the detection interface no matter whether the system is running or not. And after a result storage button is clicked, the system automatically stores the dissolution peak current and the detection result detected this time to a specified path. After the measurement termination button is clicked, the system terminates the measurement process, and at the moment, the system is in an idle state but cannot exit the system.
Specifically, the parameter setting area can perform current range setting, and can select multiple ranges of 10nA, 100nA, 1 muA, 10 muA, 100 muA, 1mA and 10 mA. Specifically, the parameter setting zone may set square wave stripping voltammetry parameters including initial potential, final potential, frequency, resting time, potential increment, amplitude, cleaning potential, cleaning time, deposition potential, and deposition time. Specifically, the parameter setting area can set different heavy metal peak recognition potential ranges, including cadmium ion dissolution potential range setting, lead ion dissolution potential range setting, bismuth ion dissolution potential range setting and copper ion dissolution potential range setting. Further, the parameter setting area can set the repeated measurement times of each detection, and the system automatically averages all detection results and uses the average value to calculate the concentration.
Specifically, the background current setting area may select whether to subtract the background current, for example, the system may automatically subtract the background current value after recognizing the peak value, and perform subsequent processing on the obtained current signal. At the same time, this area will display the background current value.
The interface is provided with an electrode cleaning module, and residual heavy metal on the surface of the electrode can be cleaned by setting cleaning potential, namely oxidation potential and cleaning time.
The operating region is selected in the detection method, and comprises a standard addition method, a conventional model method and a module of double stripping voltammetry. The sample pretreatment module is arranged in the double stripping voltammetry module.
Example 2:
FIG. 2 is a schematic diagram showing the identification and acquisition of the dissolution current of a standard solution of known heavy metal components. Preparation of Cd-containing2+、Pb2+、Cu2+、Bi3+The mixed solution of (1). Each heavy metal has its specific stripping potential, from which it is determined which heavy metal is. Shown in the figure as the stripping voltammetry diagram of heavy metal cadmium ions and lead ions. The deposition potential is-1.2V, the deposition time is 140s, the standing time is 10s, the scanning starting voltage is-1.2 Vvs. Ag/AgCl, the termination voltage is 0.2Vvs. Ag/AgCl, the potential increment is 0.005V, the pulse frequency is 25Hz, the sampling time is 0.02s, and the pulse amplitude is 0.025V. The stripping spectrum is composed of 280 data points, and after each stripping voltammetry measurement is finished, the system automatically stores output voltammetry spectrum data, namely 280 current values and corresponding potential values into an array, namely Y (N). When Y (N) -Y (N-1) > 0 and Y (N +1) -Y (N) < 0, Y (N) is the stripping current according to the scanning potential direction as shown in the figure, points A and B in figure 2The potential values corresponding to the points A and B are dissolution potentials. The system automatically calculates, identifies and obtains the peak current of the heavy metal according to the method and displays the peak current on the upper computer interface according to the dissolution potential range set on the upper computer interface. Specifically, the heavy metal elution potential range is set as follows, wherein, cadmium: -0.7V to-0.9V; lead: -0.5V to-0.7V; bismuth: -0.05V to-0.25V; copper: 0.05V to-0.05V.
Fig. 3 is a schematic diagram of a background current identification and acquisition algorithm according to an embodiment of the present invention. Shown in the figure as the stripping voltammetry diagram of heavy metal cadmium ions and lead ions. The deposition potential is-1.2V, the deposition time is 140s, the standing time is 10s, the scanning starting voltage is-1.2 Vvs. Ag/AgCl, the termination voltage is 0.2Vvs. Ag/AgCl, the potential increment is 0.005V, the pulse frequency is 25Hz, the sampling time is 0.02s, and the pulse amplitude is 0.025V. The stripping spectrum is composed of 280 data points, and after each stripping voltammetry measurement is finished, the system automatically stores output voltammetry spectrum data, namely 280 current values and corresponding potential values into an array, namely Y (N). Calculating the slope between every two adjacent data points according to the formula (1), and respectively searching two most similar slopes in the initial potential range, the stripping potential range and the potential range from the stripping potential to the tail potential according to the heavy metal stripping potential range set by the upper computer interface. And drawing tangent lines, namely a tangent line AB and a tangent line CD, by taking the points A, B and C and D with similar slopes as tangent points. And drawing a vertical line from the dissolution peak point to the X axis, wherein the value corresponding to the vertical coordinate of the intersection point of the vertical line and the vertical line is the background current value corresponding to the cadmium ions and the lead ions detected at this time.
Example 3 analysis of heavy Metal concentrations Using Standard addition method
1) Firstly clicking a connecting button, setting the use S-G smoothing, setting the maximum range to be 1mA, selecting and deducting background current, setting the repeated detection times to be 1 and setting the stripping voltage parameters as follows, wherein the deposition potential is-1.2V, the deposition time is 140S, the standing time is 10S, the scanning starting voltage is-1.2 Vvs. Ag/AgCl, the termination voltage is 0.2Vvs. Ag/AgCl, the potential increment is 0.005V, the pulse frequency is 25Hz, the sampling time is 0.02S, and the pulse amplitude is 0.025V. The heavy metal dissolution potential range is set as follows, wherein, cadmium: -0.7V to-0.9V; lead: -0.5V to-0.7V; bismuth: -0.05V to-0.25V; copper: 0.05V to-0.05V.
2) Clicking a 'first detection' button in the standard addition method module, firstly detecting the actual sample leaching liquor with unknown concentration for the first time, and automatically carrying out peak searching analysis by the upper computer control system to obtain the peak current of the target detection ions and displaying the peak current on an interface. The value of the spiked concentration is 0 at this time, i.e., no spiking is performed.
3) Quantitatively adding standard 5 mug/L to an actual sample with unknown concentration, inputting the first standard concentration 5 mug/L in an input box, clicking a 'second detection' button in a standard addition method module to perform second stripping voltammetry detection, and automatically performing peak searching analysis by an upper computer control system to obtain the peak current of the target detection ions after the first standard addition, wherein the standard concentration is 5 mug/L.
4) And quantitatively adding 10 mug/L of standard again, inputting 10 mug/L of standard adding concentration for the second time in the input box, clicking a 'third detection' button in the standard addition method module to perform third stripping voltammetry detection, and automatically performing peak searching analysis by the upper computer control system to obtain the peak current of the target detection ions, wherein the standard adding concentration is 10 mug/L.
5) And (3) performing third-time labeling on the target actual sample leaching liquor by 15 mug/L, inputting a third-time labeling concentration by 15 mug/L in an input box, clicking a 'fourth-time detection' button in a standard addition method module to perform fourth-time stripping voltammetry detection, and automatically performing peak searching analysis by an upper computer control system to obtain the peak current of target detection ions, wherein the labeling concentration is 15 mug/L.
6) After the four detections are finished, the stripping voltammograms are displayed on an interface of an upper computer in an overlapping manner, as shown in a of fig. 5. From the four elution voltammetric measurements, the peak elution values and the corresponding spiked concentrations of 0, 5. mu.g/L, 10. mu.g/L and 15. mu.g/L, a linear regression was performed using the least squares method, as shown in b and c of FIG. 5.
7) After obtaining the regression equation, the upper computer automatically obtains the absolute value of the abscissa where the peak current (ordinate Y) is 0 (i.e., shown by points a and B in B and c of fig. 5), and the absolute value is the predicted value of the concentration of the heavy metal in the sample.
8) And clicking a save button to save the detection data to the specified path.
The root mean square error, the mean absolute error, and the time required to detect a sample, which are compared with the true values of the atomic absorption spectroscopy ASS, are shown in the following table.
Example 4 analysis of heavy Metal concentration Using Standard model method
1) Firstly clicking a connecting button, setting the use S-G smoothing, setting the maximum range to be 1mA, selecting and deducting background current, setting the repeated detection times to be 1 and setting the stripping voltage parameters as follows, wherein the deposition potential is-1.2V, the deposition time is 140S, the standing time is 10S, the scanning starting voltage is-1.2 Vvs. Ag/AgCl, the termination voltage is 0.2Vvs. Ag/AgCl, the potential increment is 0.005V, the pulse frequency is 25Hz, the sampling time is 0.02S, and the pulse amplitude is 0.025V. The heavy metal dissolution potential range is set as follows, wherein, cadmium: -0.7V to-0.9V; lead: -0.5V to-0.7V; bismuth: -0.05V to-0.25V; copper: 0.05V to-0.05V.
2) FIG. 6A shows the peak values of the elution in the acetic acid buffer in the presence of cadmium ions and lead ions at 0, 1, 5, 10, 20, 30, 40, 50, 60, 70, and 80. mu.g/L, where the concentration of copper ions is 0. The fitting equations established are Y1.00603X +0.34488 and Y0.34895X +2.5064, respectively, as shown in fig. 6B and 6C.
3) When the cadmium ion is detected, the parameters 1.00603 and 0.34488 are input into the primary item coefficient position and the constant item position of the upper computer interface, and the cadmium ion is detected after the button for detecting the cadmium ion is clicked. When lead ion detection is carried out, parameters 0.34895 and 2.5064 are input to the primary term coefficient and the constant term position of an upper computer interface, and lead ions are detected after a lead ion detection button is clicked.
The root mean square error, the mean absolute error, and the time required to detect a sample, which are compared with the true values of the atomic absorption spectroscopy ASS, are shown in the following table.
Example 5 analysis of heavy Metal concentration Using double stripping voltammetry
The preparation method of the working electrode graphite powder-paraffin oil carbon paste electrode used in the embodiment comprises the following steps of; mixing graphite powder and paraffin oil, placing into a mortar, fully grinding, filling the mixture into a cavity of polytetrafluoroethylene material with the diameter of 10mm, compacting and molding, and conducting with carbon paste by taking a copper column as a lead at the rear end. And (3) polishing the surface of the carbon paste electrode by using weighing paper to obtain a smooth electrode surface.
1) Firstly clicking a connecting button, setting the use S-G smoothing, setting the maximum range to be 1mA, selecting and deducting background current, setting the repeated detection times to be 1 and setting the stripping voltage parameters as follows, wherein the deposition potential is-1.2V, the deposition time is 140S, the standing time is 10S, the scanning starting voltage is-1.2 Vvs. Ag/AgCl, the termination voltage is 0.2Vvs. Ag/AgCl, the potential increment is 0.005V, the pulse frequency is 25Hz, the sampling time is 0.02S, and the pulse amplitude is 0.025V. The heavy metal dissolution potential range is set as follows, wherein, cadmium: -0.7V to-0.9V; lead: -0.5V to-0.7V; bismuth: -0.05V to-0.25V; copper: 0.05V to-0.05V.
2) Firstly, performing predeposition treatment on a soil leaching solution, placing a three-electrode sensor consisting of a graphite powder-paraffin oil carbon paste electrode, an Ag/AgCl reference electrode and a platinum wire electrode in 500mL of the soil leaching solution, clicking a detection solution pretreatment button before detection in a double stripping voltammetry module, performing 500-700 s of first predeposition on heavy metals in the soil leaching solution by applying 0.3V constant potential, standing for 10-20 s after the deposition is finished, and taking out the three-electrode sensor to obtain the pretreated soil leaching solution.
3) And adding three ions of bismuth ions, cadmium ions and lead ions into the pretreated soil leaching liquor to ensure that the concentrations of the bismuth ions, the cadmium ions and the lead ions respectively reach 600 mu g/L, 5 mu g/L and 5 mu g/L. And placing a graphite powder-paraffin oil carbon paste electrode (which is polished and updated by using weighing paper) with updated surface area, placing a three-electrode sensor consisting of an Ag/AgCl reference electrode and a platinum wire electrode in the pretreated soil leaching liquor, clicking a first detection button to carry out first deposition, quickly transferring the three-electrode sensor into a miniature electrolytic cell to carry out first dissolution after the deposition is finished, and dripping 800 mu L of acetic acid-sodium acetate buffer solution with pH of 4.0-5.5 into the electrolytic cell in advance. And then carrying out secondary stripping voltammetry detection on the heavy metal in the micro electrolytic cell by using a three-electrode sensor consisting of a glassy carbon electrode, an Ag/AgCl reference electrode and a platinum wire electrode to obtain a stripping peak signal.
4) And (3) adding heavy metal cadmium ion and lead ion standard solutions into the pretreated soil leaching liquor to enable the concentration of the solutions to be 10 mu g/L, repeating the step (2), and clicking a second detection button to perform second stripping voltammetry detection to obtain a stripping peak signal, which is different from the step (2).
5) And (3) adding heavy metal cadmium ion and lead ion standard solutions into the pretreated soil leaching liquor to enable the concentration of the solutions to be 15 mu g/L, repeating the step (2), and clicking a third detection button to perform third stripping voltammetry detection to obtain a stripping peak signal, which is different from the step (2).
6) From the dissolution peak current values obtained by the three measurements and the corresponding spiking concentrations of 5. mu.g/L, 10. mu.g/L and 15. mu.g/L, linear regression was performed by using the least square method, and the results are shown in FIG. 7.
7) And (3) putting the three-electrode sensor into the sample solution to be detected, detecting for the fourth time, automatically identifying and obtaining the dissolution current of the heavy metal with unknown concentration in the solution to be detected by the upper computer system, substituting the dissolution current into the regression equation obtained in the step, calculating, and obtaining and displaying the detection result.
The root mean square error, the mean absolute error, and the time required to detect a sample, which are compared with the true values of the atomic absorption spectroscopy ASS, are shown in the following table.
The above examples are only for describing the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims (5)
1. The electrochemical in-situ detection method for the heavy metals in the soil is characterized by comprising the following steps:
s1, determining the dissolution peak potential of heavy metal ions by using standard solution of known heavy metal components, and determining background current; the standard solution contains cadmium, lead, bismuth and copper ions,
s2, putting a three-electrode sensor into a soil sample leaching solution, and setting Savitzky-Golay smoothening and stripping voltammetry parameters;
s3, detecting the heavy metal content by one of a standard addition method, a standard model method and a double stripping voltammetry;
wherein the operation of determining the dissolution peak potential of the heavy metal ions comprises the following steps: performing stripping voltammetry on a standard solution with known heavy metal components, wherein the obtained stripping voltammetry data is Y (N), and if Y (N) -Y (N-1) > 0 and Y (N +1) -Y (N) < 0 at the point N, the corresponding potential of the point is a stripping potential, the current of the point is a stripping current, and the stripping peak potentials of different heavy metal ions are stored in an upper computer control system;
the parameters of the stripping voltammetry measurement were: initial potential is-1.0 to-1.5 Vvs.Ag/AgCl, termination potential is 0.1 to 0.3Vvs.Ag/AgCl, frequency is 10 to 50Hz, standing time is 5 to 20s, potential increment is 0.001 to 0.01V, amplitude is 0.02 to 0.03V, cleaning potential is 0.2 to 0.5Vvs.Ag/AgCl, cleaning time is 100 plus 300s, deposition potential is-1.0 to-1.5 Vvs.Ag/AgCl and deposition time is 80 to 200 s;
the operation of determining the background current is: determining the dissolution peak potential of the heavy metal ions, wherein the dissolution peak potential within +/-0.2V is the dissolution peak potential range; according to the formula
Determining the slope between each point, wherein X (N) is the dissolution potential of each point, searching two closest slopes in the dissolution peak potential range of the heavy metal ions, connecting the two closest slopes to obtain a tangent line, drawing a vertical line perpendicular to the X axis from the dissolution peak potential, and taking the vertical coordinate of the intersection point of the vertical line and the tangent line as the background current.
2. The soil heavy metal electrochemical in-situ detection method according to claim 1, wherein the stripping voltammetry parameters set in step S2 are as follows: the deposition potential is-1.0 to-1.5V, the deposition time is 120-ion-150 s, the standing time is 5 to 15s, the scanning starting voltage is-1.5 to-1.0 Vvs. Ag/AgCl, the termination voltage is 0.1 to 0.2Vvs. Ag/AgCl, the potential increment is 0.001 to 0.01V, the pulse frequency is 20 to 30Hz, the sampling time is 0.01 to 0.05s, and the pulse amplitude is 0.02 to 0.05V.
3. The method for electrochemical in-situ detection of heavy metals in soil according to claim 1 or 2, wherein the standard addition method is operated as follows:
1) firstly, detecting actual sample leaching liquor with unknown concentration for the first time, automatically carrying out peak searching analysis by an upper computer control system to obtain the peak current of target detection ions, displaying the peak current on an interface, recording the current Y0, and carrying out standard addition with the concentration value of 0, namely carrying out standard addition;
2) quantitatively adding a standard solution into an actual sample with unknown concentration, inputting a first standard adding concentration in an input frame, carrying out second detection, and automatically carrying out peak searching analysis by an upper computer control system to obtain a peak current Y1 of a target detection ion after first standard adding, wherein the standard adding concentration is X1;
3) quantitatively adding the standard solution again, inputting the second standard adding concentration in the input frame, carrying out third detection, and automatically carrying out peak searching analysis by the upper computer control system to obtain the peak current of the target detection ion, wherein the peak current is recorded as Y2, and the standard adding concentration is 2X 1;
4) performing third-time labeling on the target actual sample leaching liquor, inputting third-time labeling concentration in an input box, performing fourth-time detection, and automatically performing peak searching analysis by an upper computer control system to obtain peak current of target detection ions, wherein the peak current is recorded as Y3, and the labeling concentration is 3X 1;
5) performing linear regression by using a least square method according to dissolution peak values Y0, Y1, Y2 and Y3 obtained by four times of detection and corresponding standard concentration;
6) after obtaining the regression equation, the upper computer automatically obtains the absolute value of the abscissa of the position where the peak current is 0, and the absolute value is the predicted value of the concentration of the heavy metal in the sample.
4. The method for electrochemical in-situ detection of heavy metals in soil according to claim 1 or 2, wherein the standard model method is operated as follows:
establishing a mathematical model of the peak value and the ion concentration by using a standard solution and taking the dissolution peak value as an independent variable and the ion concentration as a dependent variable, wherein the mathematical model is a unitary, binary or ternary equation, and the coefficient and constant term of the model are input into an upper computer control system; detecting a sample containing one to three types of modeled ions; the ions set by the model are cadmium, lead and copper ions.
5. The method for electrochemical in-situ detection of heavy metals in soil according to claim 1 or 2, wherein the operation of the double stripping voltammetry is as follows:
1) performing pre-deposition treatment on a soil leaching solution, placing a three-electrode sensor consisting of a graphite powder-paraffin oil carbon paste electrode, a reference electrode and a counter electrode in the soil leaching solution, performing 500-700 s of first pre-deposition on heavy metals in the soil leaching solution by applying a constant potential of 0.3V vsAg/AgCl, standing for 10-20 s after the deposition is finished, and taking out the three-electrode sensor to obtain the pre-treated soil leaching solution;
2) adding one or more of bismuth ions, cadmium ions and lead ions into the pretreated soil leaching liquor to enable the ion concentration to independently reach 5-600 mu g/L, carrying out first deposition, quickly transferring the three electrodes into a miniature electrolytic cell for first dissolution after the deposition is finished, adding a buffer solution with the pH value of 4.0-5.5 into the electrolytic cell in advance, and carrying out second dissolution voltammetry detection on heavy metals in the miniature electrolytic cell by using a three-electrode sensor consisting of a glassy carbon electrode, a reference electrode and a counter electrode to obtain a dissolution peak signal X0;
3) adding heavy metal with known concentration into the pretreated soil leaching liquor, wherein the concentration of the solution is Y1, repeating the step 1) to perform second stripping voltammetry detection to obtain a stripping peak signal X1;
4) adding heavy metal with known concentration into the pretreated soil leaching liquor, wherein the concentration of the solution is Y2, repeating the step 1) to carry out third stripping voltammetry detection to obtain a stripping peak signal X2;
5) performing linear regression by using a least square method according to concentration values Y0, Y1 and Y2 obtained by three times of detection and corresponding standard concentration X0, X1 and X2;
6) and (3) putting the three-electrode sensor into the sample solution to be detected, detecting for the fourth time, automatically identifying and obtaining the dissolution current of the heavy metal with unknown concentration in the solution to be detected by the upper computer system, substituting the dissolution current into the regression equation obtained in the step, calculating, and obtaining and displaying the detection result.
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| CN110907520B (en) * | 2018-09-17 | 2020-12-01 | 中国农业大学 | Device for detecting ion concentration in soil leaching solution and using method thereof |
| CN111426738B (en) * | 2020-03-14 | 2022-12-02 | 华中师范大学 | Electrochemical in-situ monitoring device and method for soil/underground water remediation process |
| CN111505096A (en) * | 2020-04-27 | 2020-08-07 | 华虹半导体(无锡)有限公司 | Metal ion monitoring system |
| CN113252744B (en) * | 2021-05-11 | 2023-03-14 | 中南大学 | Photoelectrochemistry-based detector for trace ions/molecules in solution |
| CN113984477B (en) * | 2021-11-02 | 2023-10-13 | 南京农业大学 | Electrochemical detection method for concentration of organic heavy metal in soil |
| CN114923975A (en) * | 2022-04-01 | 2022-08-19 | 江苏大学 | Method for monitoring cadmium ions in tea tree leaves on line by using flexible sensing film |
| CN116223580B (en) * | 2022-12-28 | 2023-10-20 | 中山大学 | Arsenic pollution in-situ detection system and method |
| CN117147667B (en) * | 2023-10-30 | 2024-01-19 | 中国农业大学 | Method and system for detecting weak acid soluble heavy metal in soil |
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